Steerable or deflectable tip cardiovascular catheters are useful in many applications, being a marked improvement over catheters with fixed tips. They are especially useful in the field of electrophysiology for performing radio frequency ablation of cardiac tissue to interrupt abnormal electrical pathways in the heart.
There are presently several useful designs of steerable tip catheters. One such steerable tip catheter is described in Reissue Pat. No. 34,502. The catheter has an elongated catheter body and tip portion which can be deflected into a semi-circle in one direction. In addition, the catheter body and tip portion can be rotated. Therefore by tip deflection, catheter rotation and catheter translation, i.e., lengthwise movement of the catheter, contact of the tip portion with most areas of a heart chamber may be made.
There are, however, structures and irregularity in the heart chambers which often make access to a particular location difficult. In some cases it is necessary to reach around obstacles to contact a desired site. Moreover, it may be necessary to use a longer or shorter deflectable tip portion to reach a particular site and maintain adequate stable contact.
One early multidirectional deflectable tip catheter had a catheter body and tip with 5 lumens, i.e., a central lumen and four outer lumens disposed symmetrically around the central lumen. This catheter had four puller wires which extended through the outer lumens. The distal ends of the puller wires were attached to a ring at the tip and the proximal ends were attached to a "joy stick". The central lumen was open at its distal end and connected to a luer hub at its proximal end. This catheter had no reinforcement in its body or tip. It was not suitable for electrophysiology because it had effectively no torque transmission to the tip which made tip rotation difficult. Moreover, the catheter body was subject to the same deflection as the tip, but to a lesser degree.
A more recent steerable catheter has a steerable tip that is controlled by a bendable control handle. Multiple puller wires connect the steerable tip to this control handle which can be bent in any direction and can be thought of as a multiple ball joint with friction. The tip, once deflected, can be further deflected laterally by an internal stylette. The disadvantage of this catheter design is that the tip is very soft and has poor lateral stiffness due to the presence of the stylette which cannot transmit torque effectively. Because of this, an electrode at the tip of the catheter cannot be held firmly against the myocardial wall.
Another recent steerable tip catheter comprises a deflectable tip which can be deflected in one direction by a puller wire and further deflected laterally by an internal stylette. The stylette can also be moved axially within the catheter to change the shape of the tip curvature.
The disadvantage of this catheter design is that the lateral stiffness of the tip is dependent upon the stylette which cannot transmit torque effectively.
In a design wherein the tip is rotated by means of a stylette, it follows that the lateral stiffness of the tip must be less than that of the stylette alone. This is because some torque from the stylette is required to rotate the tip. Moreover, the stylet must be kept small to allow the catheter body and tip to bend and to be safe within the patient body and heart.